Drilling wells for oil and gas recovery, as well as for other purposes, involves the use of drill pipes which, at one end, are equipped with a drilling bit whose function is to cut through various types of rock formations. The most severe abrasive wear conditions occur when drilling through highly siliceous geological earth formations. A rotational movement of the pipe ensures the progression of drilling. Pipes such as commonly used today come in sections of about 30 feet in length. These sections are connected to one another by means of tool joints. Typically these tool joints, which themselves are protected against wear by abrasion resistant overlays, have a diameter significantly larger than the body of the pipes. Under conditions of vertical drilling the tool joints protect the body of the pipes quite efficiently.
More recent technology has evolved, utilizing directional drilling, meaning the deviation of drilling from vertical to horizontal over more or less large bending radiuses of curvature. Coupled with the use of increased pipe section lengths of about 45 feet and larger diameters relative to the tool joint diameter, the fact is that the tool joints offer a lesser degree of protection of the body of the pipe and that the direct interaction of the pipe body with the walls of the well is more likely to occur. The consequence is an exposure of the pipe to wear mechanisms that may affect its integrity to a significant degree. When drilling into mineral formations, the wear mechanism involved is mainly abrasion. When drilling takes place into a steel casing or marine riser (where a marine riser connects a floating drilling or production unit to the wellhead(s) on the sea floor and through which the drill pipe passes), the wear mechanism is predominantly metal-to-metal wear with interposition of drilling fluids and drill cuttings. These wear situations are also encountered with other downhole equipments such as coiled tubing, downhole tools housing expensive instrumentation and other components exposed to longitudinal and rotational wear during well drilling operations.
One prior attempted solution was placing clamps in the middle of a drill pipe joint to keep the drill pipe away from the surface of the well bore. However, this attempted solution resulted in a catastrophic failure that led to litigation, because the clamps allegedly either separated from the pipe downhole or caused drill pipe failure. Another attempted solution was clamping rubber sleeves on the drill pipe, which also has not been successful. Further, paints, epoxy coatings, and powder metallurgy resists oxidation, but are very unsuitable for the abrasion encountered in drilling through rock. Another proposed solution was patented in U.S. Pat. No. 4,665,996 based on a particular alloy. The patent teaches essentially a welding or fusion process, either through hardsurfacing or by transfer plasma arc, respectively, for a particular material alloyed to the base material of the drill pipe to reduce wear and friction. Either process results in a metallurgical change of the base material of the drill pipe by essentially localized melting of a base material surface to add the alloy. It is believed that this concept was not successful commercially, probably due to the fact that such processes are generally avoided as welding or fusion on the drill pipe with the intense heat. Such processes may cause metallurgical changes in the base material and possible failure in the well bore that can cause the loss of millions of dollars in deeper wells. Also, the alloys referenced in this patent are expensive cobalt-based alloys that require the use of intermediate, or so-called buffer layers, of high-alloyed austenitic steels.
Further, such processes would be fatal to downhole tools having instrumentation therein, where a downhole instrumentation tool can cost up to about half a million dollars. Typically, the inside surfaces of drill pipe are coated with a corrosion resistant layer that may be damaged by the high temperatures generated during any external application by welding or fusion processes.
U.S. Pat. No. 3,012,881 ('881 patent) teaches spraying an alloy onto a part to which the alloy will not adhere or stick, and then melting the sprayed alloy while on said part. The particular alloy disclosed melts at a temperature of about 2050° F. (1120° C.). Thus, the '881 patent is similarly situated as the above '996 patent that requires higher temperatures and could cause metallurgical changes to the base material of the part and possible failure of the part downhole.
U.S. Pat. No. 4,630,692 ('692 patent) teaches a method of forming a cutter, which includes a core and a wear resistant insert defining a body means which includes (a) applying to the body means a mixture of: (i) wear resistant metallic powder, and (ii) binder (b) volatilizing the binder, (d) and applying pressure to the body means and powdered metal, at elevated temperature to consolidate same. The '692 applies the powder by dipping, painting, or spraying to temporarily hold the material to the part until the perform is heated and hot pressed at an elevated temperature in the range of 1900° to 2300° F. (1040 to 1260° C.). While the teaching may produce a wear resistant layer, it uses entirely powder metallurgy technology with associated pressing and further uses relatively high temperatures that can affect metallurgical properties of the base material.
U.S. Pat. Publication. No. 2001/0030067 ('067), teaches mounting a plurality of thermally stable polycrystalline diamond (TSP) bearing elements through welding, brazing, or adhesives, or by mechanically holding in place to form a wear resistant surface. Then, a settable facing material is applied to the part surface which bonds to the surface between the bearing elements and embraces the TSP bearing elements to hold them in place. The '067 patent teaches a method in which TSP bearing elements are secured to a component surface such as by welding or brazing part of the surface of each TSP bearing element to the component and are at least partly surrounded by a layer of less hard material. The less hard material can be flame sprayed, electrically plated, physical vapor deposited, or metal sprayed onto the surface. The wearable layer can be deposited to the height of the TSP elements, or overlayed and ground away to expose the TSPs or left to wear away during use to expose the TSPs in downhole use. Thus, this reference provides a wear resistant layer of TSPs by welding or brazing, or temporarily by adhesives or mechanically holding in place, until the wearable filler material can be deposited therebetween.
Another reference, Lampman S.R. and Reidenbach: “AMS HandbooK: Surface Engineering” 1994, US Metals Park, ASM International, USA 5, XP002366720, “Thermal Spray Coatings,” pages 497-500 describes the term “thermal spray” as a generic term for a group of processes in which metallic, ceramic, cermet, and some polymeric materials in the form of powder, wire, or rod are fed to a torch or gun with which they are heated to near or somewhat above their melting point. The resulting molten or nearly molten droplets of materials are projected against the surface to be coated. Upon impact, the droplets flow into thin lamellar particles adhering to the surface, overlapping and interlocking as they solidify. The total coating thickness is usually generated in multiple passes of the coating device. The articles describes thermal spray types of flame spraying, flame spray and fuse, electric-arc (wire-arc) spray, and plasma spray. The article states that flame spray exhibits lower bond strengths, higher porosity, and a higher heat transmittal to the substrate relative to other types. The type known as flame spray and fuse is a modification of a cold spray method where parts are prepared and coated with the coating materials and then fused by heating to a temperature of 1850° to 2150° F. (1010° to 1175° C.). The articles states that fusing temperatures may alter the heat-treated properties of some alloys. The article also describes electric-arc (wire-arc) spray as a process that has no external heat source such as a gas flame or electrically induced plasma. Rather, it uses two electrically opposed charged wires, comprising the spray materials that are fed together in such a manner that a controlled arc occurs at the intersection. The molten metal on the wire tips is atomized and propelled onto a prepared substrate by a stream of compressed air or other gas. However, this article does not address known issues using this process of a peeling away of thicker layers from the base material, especially under wear conditions, for example, when the layers are 0.10 inches (2.5 millimeters) and greater. Finally, the article discusses plasma spray, in which a gas is allowed to flow between a tungsten cathode and a water-cooled copper anode. An electric arc is initiated between the two electrodes that ionizes the gas to create temperatures exceeding 54,000° F. (30,000° C.). Powder is introduced into the gas stream, heated, and accelerated toward a substrate base material for deposit thereon. The article describes coating thicknesses usually ranging from about 0.002 to 0.020 inches (0.05 to 0.50 millimeters), and further states that thicker coatings can be formed for some applications such as dimensional restoration or thermal barriers. Similarly, the article does not address known issues using this process of peeling away of thicker layers from the base material, especially under wear conditions.
Thus, there remains a need to provide a commercially effective protective wear resistant layer on downhole equipment.